1. Technical Field
The present invention relates to a vibration control structure for suppressing (controlling) vibration of a steering wheel in which an airbag device is incorporated.
2. Related Art
When vibration in a vertical direction or lateral direction is transmitted to a steering wheel during high-speed travelling of a vehicle or idling of an in-vehicle engine, the vibration is transmitted to a driver through his hands grasping the steering wheel and therefore a comfortable driving may be impaired. For this reason, techniques for suppressing (controlling) vibration of the steering wheel have been developed and proposed in the prior art. Among these techniques, there is a technique that uses a dynamic damper composed of a weight and an elastic member for supporting the weight on a cored bar or the like of the steering wheel. According to this technique, when vibration of frequency being the same or close to the specific resonance frequency of the dynamic damper is transmitted from the steering wheel to the dynamic damper, the dynamic damper is resonated to absorb the vibration energy of the steering wheel. With this absorption, the vibration of the steering wheel is suppressed (controlled).
Meanwhile, an airbag device is incorporated in the steering wheel so as to protect a driver at the time of collision of a vehicle or the like. The airbag device includes an airbag and an inflator for supplying gas to the airbag. In the airbag device, the airbag is inflated rearward by the gas supplied from the inflator at the time of collision of a vehicle or the like and therefore a driver is protected from impact.
Here, since the airbag device occupies a substantial portion of an internal space of the steering wheel, it is difficult to incorporate the above-described dynamic damper in a recent steering wheel.
Therefore, a steering wheel has been proposed in which an airbag device serves as a dynamic damper (for example, see JP-A-2012-158236).
As shown in FIG. 18, the steering wheel includes a fixed member (horn plate) 51, an airbag device 52, a horn switch mechanism 53 and an elastic member 54. The fixed member (horn plate) 51 is fixed to a steering shaft (not shown) extending in a longitudinal direction (front-rear direction) and has a mounting hole (opening) 55. The airbag device 52 includes a bag holder (base plate) 56 and is disposed on the rear side of the fixed member (horn plate) 51.
The horn switch mechanism 53 includes a support member (guide member) 57 and a slider (bush) 58. The support member (guide member) 57 extends forwardly in a state of being mounted to the bag holder (base plate) 56 and is inserted through the mounting hole (opening) 55 of the fixed member (horn plate) 51. The slider (bush) 58 is disposed between the support member (guide member) 57 and the mounting hole (opening) 55 so as to be slidable in a longitudinal direction (front-rear direction). In the horn switch mechanism 53 with such a configuration, a horn device is actuated by a relative movement between the slider (bush) 58 and the bag holder (base plate) 56 due to a pressing operation of the airbag device 52.
The elastic member 54 has an annular shape and is mounted to the slider (bush) 58. The elastic member 54 is mounted to the fixed member (horn plate) 51 at the mounting hole (opening) 55.
Meanwhile, the part names in parentheses correspond to the part names that are used in JP-A-2012-158236.
According to the above-described steering wheel, the airbag device 52 serves as a damper mass of the dynamic damper and the elastic member 54 serves as a spring of the dynamic damper. Therefore, when the steering wheel is vibrated at a predetermined frequency in a direction (such as a vertical direction or a lateral direction) perpendicular to a steering shaft, the elastic member 54 is vibrated together with the airbag device 52 in a direction perpendicular to the steering shaft while being elastically deformed at a resonance frequency that is the same or close to the predetermined frequency, thereby absorbing the vibration energy of the steering wheel. With this absorption, the vibration of the steering wheel is suppressed (controlled).
However, in a configuration disclosed in JP-A-2012-158236, in order to mount the elastic member 54 to the fixed member (horn plate) 51, a groove 59 is provided in an outer peripheral portion of the elastic member 54 and fitted to an insulator 61 mounted to the mounting hole (opening) 55. For this reason, in a structure where the elastic member 54 is mounted to the fixed member (horn plate) 51 only at the outer peripheral portion thereof as described above, it is hard to say that the mounting strength of the elastic member 54 relative to the fixed member (horn plate) 51 is sufficiently high. Further, since the elastic member 54 having an outer diameter greater than an inner diameter of the mounting hole (opening) 55 is mounted to the mounting hole (opening) 55, an operation for mounting the elastic member 54 to the fixed member (horn plate) 51 is complicated.
The present invention has been made in consideration of the above-described situations and an object thereof is to provide a vibration control structure for a steering wheel, which is capable of mounting an elastic member with high strength by performing a simple operation.